1. Field of the Invention
The present invention relates to the preparation of .beta.,.gamma.-unsaturated carboxylic acids by reacting conjugated dienes and carbon monoxide in the presence of water.
2. Description of the Prior Art
It is known to this art, from French Patent No. 1,406,194, that 3-pentenoic acid can be prepared by reacting butadiene, carbon monoxide and water in the presence of bis-triphenylphosphine-palladium dichloride and hydrochloric acid at a temperature on the order of 120.degree. to 140.degree. C., under a pressure on the order of 700 bar.
However, in spite of the high pressures used, this process is of low efficiency and its selectivity as regards the desired acid is unsatisfactory.
It too is known, from French Patent No. 1,476,301, that 3-pentenoic acid can be prepared by reacting butadiene, carbon monoxide and water in the presence of palladium, hydrochloric acid and oxygen at a temperature of 100.degree. C., under a pressure on the order of 700 bar. Although an appreciable amount of 3-pentenoic acid is obtained under these conditions, this particular method is unsatisfactory, especially because it entails use of a dangerous mixture of carbon monoxide and oxygen and the increase in the risk of corrosion connected with the simultaneous presence of water, hydrochloric acid and an oxidant in the reaction mixture. Furthermore, in spite of the high pressures used, this process remains of low efficiency and its selectivity as regards the desired acid is unsatisfactory
The above reaction (carbonylation of conjugated dienes in the presence of water) is also described in U.S. Pat. No. 3,509,209. This reaction is carried out in the presence of palladium and hydrochloric acid and, if appropriate, iron compounds. However, this technique is not satisfactory because, in particular, of the low level of conversion found for the diene and its low selectivity as regards the desired acid.
It has, moreover, also been found that if the reaction of butadiene, carbon monoxide and water is carried out in the presence of palladium-II chloride and hydrochloric acid, the complex catalyst is unstable and deteriorates into granules of inactive palladium metal.